In order for T cells to respond to foreign proteins, two signals must be provided by antigen-presenting cells (APCs) to resting T lymphocytes (Jenkins, M. and Schwartz, R. (1987) J. Exp. Med. 165:302-319; Mueller, D. L. et al. (1990) J. Immunol. 144:3701-3709). The first signal, which confers specificity to the immune response, is transduced via the T cell receptor (TCR) following recognition of foreign antigenic peptide presented in the context of the major histocompatibility complex (MHC). The second signal, termed costimulation, induces T cells to proliferate and become functional (Lenschow et al. (1996) Annu. Rev. Immunol. 14:233). Costimulation is neither antigen-specific, nor MHC restricted and is thought to be provided by one or more distinct cell surface molecules expressed by APCs (Jenkins, M. K. et al. (1988) J. Immunol. 140:3324-3330; Linsley, P. S. et al. (1991) J. Exp. Med. 173:721-730; Gimmi, C. D., et al. 1991 Proc. Natl. Acad. Sci. USA 88:6575-6579; Young, J. W. et al. (1992) J. Clin. Invest. 90:229-237; Koulova, L. et al. (1991) J. Exp. Med. 173:759-762; Reiser, H. et al. (1992) Proc. Natl. Acad. Sci. USA 89:271-275; van-Seventer, G. A. et al. (1990) J. Immunol. 144:4579-4586; LaSalle, J. M. et al. (1991) J. Immunol. 147:774-80; Dustin, M. I. et al. (1989) J. Exp. Med. 169:503; Armitage, R. J. et al. (1992) Nature 357:80-82; Liu, Y. et al. (1992) J. Exp. Med. 175:437-445).
The CD80 (B7-1) and CD86 (B7-2) proteins, expressed on APCs, are critical costimulatory molecules (Freeman et al. (1991) J. Exp. Med. 174:625; Freeman et al. (1989) J. Immunol. 143:2714; Azuma et al. (1993) Nature 366:76; Freeman et al. (1993) Science 262:909). B7-2 appears to play a predominant role during primary immune responses, while B7-1, which is upregulated later in the course of an immune response, may be important in prolonging primary T cell responses or costimulating secondary T cell responses (Bluestone (1995) Immunity 2:555).
One receptor to which B7-1 and B7-2 bind, CD28, is constitutively expressed on resting T cells and increases in expression after activation. After signaling through the T cell receptor, ligation of CD28 and transduction of a costimulatory signal induces T cells to proliferate and secrete IL-2 (Linsley, P. S. et al. (1991) J. Exp. Med. 173:721-730; Gimmi, C. D. et al. (1991) Proc. Natl. Acad Sci. USA 88:6575-6579; June, C. H. et al. (1990) Immunol. Today. 11:211-6; Harding, F. A. et al. (1992) Nature 356:607-609). A second receptor, termed CTLA4 (CD 152) is homologous to CD28 but is not expressed on resting T cells and appears following T cell activation (Brunet, J. F. et al. (1987) Nature 328:267-270). CTLA4 appears to be critical in negative regulation of T cell responses (Waterhouse et al. (1995) Science 270:985). Blockade of CTLA4 has been found to remove inhibitory signals, while aggregation of CTLA4 has been found to provide inhibitory signals that downregulate T cell responses (Allison and Krummel (1995) Science 270:932). The B7 molecules have a higher affinity for CTLA4 than for CD28 (Linsley, P. S. et al. (1991) J. Exp. Med. 174:561-569) and B7-1 and B7-2 have been found to bind to distinct regions of the CTLA4 molecule and have different kinetics of binding to CTLA4 (Linsley et al. (1994) Immunity 1:793). A new molecule related to CD28 and CTLA4, ICOS, has been identified and seems to be important in IL-10 production (Hutloff et al. (1999) Nature 397:263; WO 98/38216), as has its ligand, which is a new B7 family member (Aicher A. et al. (2000) J. Immunol. 164:4689-96; Mages H. W. et al. (2000) Eur. J. Immunol. 30:1040-7; Brodie D. et al. (2000) Curr. Biol. 10:333-6; Ling V. et al. (2000) J. Immunol. 164:1653-7; Yoshinaga S. K. et al. (1999) Nature 402:827-32). If T cells are only stimulated through the T cell receptor, without receiving an additional costimulatory signal, they become nonresponsive, anergic, or die, resulting in downmodulation of the immune response.
The importance of the B7:CD28/CTLA4 costimulatory pathway has been demonstrated in vitro and in several in vivo model systems. Blockade of this costimulatory pathway results in the development of antigen specific tolerance in murine and human systems (Harding, F. A. et al. (1992) Nature 356:607-609; Lenschow, D. J. et al. (1992) Science 257:789-792; Turka, L. A. et al. (1992) Proc. Natl. Acad. Sci. USA 89:11102-11105; Gimmi, C. D. et al. (1993) Proc. Natl. Acad. Sci. USA 90:6586-6590; Boussiotis, V. et al. (1993) J. Exp. Med. 178:1753-1763). Conversely, expression of B7 by B7 negative murine tumor cells induces T-cell mediated specific immunity accompanied by tumor rejection and long lasting protection to tumor challenge (Chen, L. et al. (1992) Cell 71:1093-1102; Townsend, S. E. and Allison, J. P. (1993) Science 259:368-370; Baskar, S. et al. (1993) Proc. Natl. Acad. Sci. 90:5687-5690.). Therefore, manipulation of the costimulatory pathways offers great potential to stimulate or suppress immune responses in humans.
The present invention is based, at least in part, on the discovery that PD-1 is a receptor for B7-4 molecules expressed on antigen presenting cells. PD-1 transmits a negative signal to immune cells, similar to CTLA4. B7-4 molecules are expressed on the surface of antigen presenting cells and provide a costimulatory signal to immune cells and can transmit downmodulatory signals to immune cells, depending upon the molecule to which they bind. Thus, modulation of PD-1, B7-4, and/or the interaction between B7-4 and PD-1 results in modulation of the immune response.
Accordingly, in one aspect, the invention provides a method for modulating an immune response comprising contacting an immune cell with an agent that modulates signaling via PD-1 to thereby modulate the immune response.
In one embodiment, the immune response is downregulated.
In another embodiment, signaling via PD-1 is stimulated using an agent selected from the group consisting of: an activating antibody that recognizes PD-1, a form of B7-4 that binds to an inhibitory receptor, and a small molecule that binds to PD-1.
In one embodiment, the immune cell is selected from the group consisting of: a T cell, a B cell, and a myeloid cell.
In one embodiment, anergy is induced in the immune cell.
In one embodiment, the method further comprising contacting the immune cell with an additional agent that downregulates an immune response.
In one embodiment, the immune response is upregulated.
In one embodiment, the signaling via PD-1 is inhibited using an agent selected from the group consisting of: a blocking antibody that recognizes PD-1, a non-activating form of B7-4, an antibody that recognizes B7-4, and a soluble form of PD-1.
In one embodiment, the step of contacting occurs in vivo. In another embodiment, the step of contacting occurs in vitro.
In another aspect, the invention pertains to a method for modulating the interaction of B7-4 with an inhibitory receptor on an immune cell comprising contacting an antigen presenting cell which expresses B7-4 with an agent selected from the group consisting of: a form of B7-4, a form of PD-1, or an agent that modulates the interaction of B7-4 and PD-1 such that the interaction of B7-4 with an inhibitory receptor on an immune cell is modulated.
In one embodiment, the method further comprises contacting the immune cell or the antigen presenting cell with an additional agent that modulates an immune response.
In one embodiment, the step of contacting is performed in vitro. In another embodiment, the step of contacting is performed in vivo.
In one embodiment, the immune cell is selected from the group consisting of: a T cell, a B cell, and a myeloid cell.
In another aspect, the invention pertains to a method for inhibiting activation in an immune cell via a non-apoptotic mechanism comprising increasing the activity or expression of PD-1 in a immune cell such that immune cell activation is inhibited.
In another aspect, the invention pertains to vaccine comprising an antigen and an agent that inhibits signaling via PD-1 in an immune cell.
In another aspect, the invention pertains to a composition comprising an antigen and an agent that promotes signaling via PD-1 in an immune cell.
In another aspect, the invention pertains to a method for treating a subject having a condition that would benefit from upregulation of an immune response comprising administering an agent that inhibits signaling via PD-1 in a immune cell of the subject such that a condition that would benefit from upregulation of an immune response is treated.
In one embodiment, the agent comprises a soluble form of PD-1 or B7-4.
In one embodiment, the method further comprises administering a second agent that upregulates an immune response to the subject.
In one embodiment, the condition is selected from the group consisting of: a tumor, a neurological disease or an immunosuppressive disease.
In another aspect, the invention pertains to a method for treating a subject having a condition that would benefit from downregulation of an immune response comprising administering an agent that stimulates signaling via PD-1 in a immune cell of the subject such that a condition that would benefit from downregulation of an immune response is treated.
In one embodiment, said agent is selected from the group consisting of: an antibody that stimulates signaling via PD-1, a bispecific antibody, and soluble B7-4.
In one embodiment, the method further comprises administering a second agent that downregulates an immune response to the subject.
In one embodiment, the condition is selected from the group consisting of: a transplant, an allergy, and an autoimmune disorder.
In another aspect, the invention pertains to a cell-based assay for screening for compounds which modulate the activity of B7-4 or PD-1 comprising contacting a cell expressing a B7-4 target molecule or PD-1 target molecule with a test compound and determining the ability of the test compound to modulate the activity of the B7-4 or PD-1 target molecule.
In yet another aspect, the invention pertains to a cell-free assay for screening for compounds which modulate the binding of B7-4 or PD-1 to a target molecule comprising contacting a B7-4 or PD-1 protein or biologically active portion thereof with a test compound and determining the ability of the test compound to bind to the B7-4 or PD-1 protein or biologically active portion thereof.